1. Field of the Invention
This invention relates to a device for obtaining rapid ignition of a gas burner of a cooking hob in accordance with the introduction to the main claim.
2. Description of the Related Art
Gas cooking hobs are known to comprise a plurality of burners each fed by its own gas pipe. Each burner is controlled by a corresponding knob and is associated with a known spark generator (or igniter) controlled via the said knob or via an independent pushbutton. The gas pipe can be of valved type or non-valved type. The non-valved type does not comprise any safety member for shutting off the gas flow to the burner. The valved pipe is instead provided with a small solenoid valve in series with the usual valve or cock operated by the knob. If the flame is accidentally extinguished the solenoid valve in series with the cock closes to hence interrupt the escape of unburnt gas from the burner. In this manner a safety function is achieved on the cooking hob.
The operation of this solenoid valve is triggered by a thermocouple or similar member (immersed in the flame) acting as a voltage generator. When the flame is present, the thermocouple generates a voltage sufficient to maintain the solenoid valve open, whereas when the flame disappears the voltage generated falls below the minimum necessary to maintain the solenoid valve open, so causing it to close and interrupt gas flow.
This solution is negatively influenced by the thermal inertia involved in heating the thermocouple. In this respect the voltage generated depends exclusively on the temperature of the thermocouple cold joint. This temperature is itself dependent on the thermal mass of the thermocouple and its housing. On accidental extinguishing, this thermal inertia shows as a delay in closing the solenoid valve after the disappearance of the flame. On ignition, this delay is much more apparent and results in lack of user satisfaction. In this respect, to ignite a burner having a solenoid valve in its feed pipe in which the corresponding knob activates the igniter, the user has to first press (applying a fairly large force) and rotate the knob controlling the gas cock and maintain it pressed for the time required to ignite the flame and then heat the thermmocouple. If the knob is released before the thermocouple attains a temperature sufficient to maintain the solenoid valve in its open position, the flame goes out and the user has to again act in the aforesaid manner to attempt a second ignition.
The situation is further worsened by the fact that on the cooking hob there is nothing to indicate to the user when the thermocouple is sufficiently hot for the knob to be released, so that there is a high probability of its early release with consequent extinguishing of the flame. This means that involuntary extinguishing is one of the causes of widespread user dissatisfaction with currently available cooking hobs.
An object of the invention is to provide a device for obtaining rapid ignition of a cooking hob burner fed via a gas pipe provided with a solenoid valve or safety valve.
A particular object of the invention is to provide a device of the aforesaid type which enables the safety valve positioned in the gas pipe to be activated immediately on operation of the burner control knob by a user, by nullifying the waiting time for this activation related to the heating of the thermocouple associated with the burner. In this way the user is saved the annoying initial stage in burner activation in which said knob has to be kept pressed, and avoids the possibility of the user releasing the knob before the required time and causing the flame to go out, so that a second ignition has to be attempted.
These and further objects which will be apparent to an expert of the art are attained by a device in accordance with the accompanying claims.